The determination of Coulomb parameters (cohesion and angle of internal shearing resistance), which are needed in the Coulomb equation for the calculation of shearing stress of soil, is essential for the application of classical soil mechanics theory to construction and stability problems. Normal procedures require taking two or three undisturbed core samples of soil, carrying them to a laboratory and determining shear strength at different values of confining pressure in order to define the Coulomb relationship from which the shearing stress may be calculated. It may take two or three days to conduct these laboratory tests and to make the results known at the construction site. Also, these tests are relatively expensive. It is therefore desirable that the shearing stress tests be made at the natural site of the soil so that the results may be quickly calculated and put to use and so that the cost per test is reduced.
Most site testing methods have had the disadvantage that cohesion and angle of internal shearing resistance were not capable of being separately measured. For example, in the vane shear test, a bladed vane is pushed into the sediment and a torque is applied to cause circumferential shearing. However, the vane shear test principally measures cohesion. Attempts to measure internal friction angle have not been generally successful.
Some instruments, such as the Torvane shear strength instrument, merely provide an index reading which can be compared with other readings to determine which soil is weaker. The Torvane instrument's reading also cannot be compared to the cohesion of the soil or the angle of internal shearing resistance. Furthermore, no specific units or dimensions can be assigned nor can the strength of the soil be determined. Cone penetrometers give an indication of the strength of the soil but do not give usable information concerning the behavior thereof. Thus, conventional devices for soil testing at the site of the soil have not been able to determine shearing stresses in the soil.
It is therefore a primary objective of the present invention to provide an inexpensive means and a quick and easy method for accurately measuring the Coulomb parameters of soil at the original site of the soil.
It is a further objective of the present invention to provide a device that is economical to manufacture and durable in use.
These and other objectives will become apparent in the description of the present invention.